Aqueous suspensions of titanium dioxide and cationic amylaceous matter, intended for the production of paper and cardboard

ABSTRACT

Novel aqueous suspensions containing a very specific filler/binder pair, in particular a filler based on titanium dioxide and a binder in the form of a liquid composition of cationic amylaceous material having very specific characteristics in terms of dry matter, viscosity, nitrogen content and pH. A method for producing the suspensions, the use of the suspensions for the production of paper and cardboard and the resulting paper and cardboard are also described.

The present invention relates to novel aqueous suspensions containing a very specific filler/binder pair, in particular a filler which is based on titanium dioxide, and in particular a binder in the form of a liquid composition of cationic amylaceous material having very specific characteristics in terms of dry matter, viscosity, nitrogen content and pH.

A sheet of paper or of cardboard is a support produced from cellulose fibers. These fibers are mainly extracted from wood or from paper and cardboard recovered in order to be recycled. The production of such a sheet involves several steps. In a first step, the paper pulp is produced: this operation consists in separating the cellulose fibers, half derived from wood and/or from recovered paper and cardboard. The “wood” pulps are derived from a mechanical, thermomechanical or chemical treatment of the wood; the “recycled” homologs thereof are obtained by suspending the recovered paper and cardboard in water, and then purifying and deinking.

In a second step, the pulp is diluted in water before reaching the paper machine. It then reaches the head box of the machine, which uniformly distributes the fibers and gives the flow of the paste in suspension its geometry. Current production is carried out by means of gigantic machines more than 100 m long and up to 10 m wide. The sheet is produced at a speed ranging up to 1800 m/min. A paper machine represents a considerable investment (the cost of a new machine is close to a billion euros).

This step corresponds to the “wet end” of the production of the sheet of paper. At this level, various constituents can be added to the fibers, which will therefore be an integral part of the sheet produced. Among them, mention may be made of pigments and fillers which may be inorganic or organic, such as titanium dioxide which is then used for the production of decorative papers, but also calcium carbonate or talc. In the remainder of the application, the simple term “fillers” will denote both pigments and fillers, irrespective of whether the latter are of inorganic or organic origin.

Documents EP 2 075 374, EP 2 143 688 and EP 2 455 429 illustrate the use of aqueous suspensions of essentially carbonate-based inorganic materials as bulk filler, the latter expression referring to the wet end of the production of the sheet of paper. With regard to EP 1 989 264, it relates quite particularly to the use of titanium dioxide for the production of decorative paper. In addition to the fillers, binders may also be introduced into this wet end. Reference may be made, for example, to U.S. Pat. No. 5,147,908 which discloses the use of polyvinyl alcohol to this effect.

It is then necessary to remove the water so as to structure the sheet of paper. To do this, said sheet undergoes successive operations involving draining, pressing, passing between rolls and, finally, drying. A sheet is finally obtained, the moisture content of which does not exceed 5% by weight of water.

Finally, the sheet of paper can undergo “coating” operations. In this case, a coating operation is carried out, consisting in depositing at the surface of the support a complex formulation called a “coating color”. The latter contains water, at least one filler, at least one binder, and also various other additives chosen in particular from a dispersant, a rheology modifier, an optical brightener, an antifoam, etc. Titanium dioxide is a particularly advantageous filler when a significant degree of whiteness and good opacity are desired.

It therefore appears that two key steps of the production of a coated sheet of paper or of cardboard involve two common constituents: both the binder and the filler, including quite particularly titanium dioxide, are in fact found in the wet end and in the coating of the sheet. It is already well known to carry these two constituents together, in particular in the form of an aqueous suspension.

The stability of such suspensions, linked in particular to the state of dispersion of the pigment and of the binder in the aqueous phase, is a very significant characteristic if said suspensions must be stored for long periods. Furthermore, it is today sought to replace binders resulting from petrochemistry with solutions of vegetable origin. Finally, it is well known that the electric charge of the filler greatly influences the printability properties of paper and cardboard.

As it happens, the applicant has today developed novel aqueous suspensions which contain a very specific pair, containing a filler which is based on titanium dioxide and a liquid composition of cationic amylaceous material (that is to say a liquid composition containing a cationic starch) having very specific characteristics in terms of dry matter, viscosity, nitrogen content and pH.

Surprisingly and particularly advantageously, these suspensions prove to be particularly stable over time. Furthermore, the use of starch meets the market demand, the desire of which is to move toward binders of biobased origin. Finally, papers produced by using such suspensions, whether in the wet end or in coating, have excellent printability properties.

Thus, a first subject of the present invention consists of an aqueous suspension containing:

-   -   a) water,     -   b) a filler which is titanium dioxide,     -   c) a liquid composition of cationic amylaceous material having:         -   a dry matter by weight of between 10% and 50%,         -   a viscosity, determined according to a T test, of greater             than 200 mPa·s and at most equal to 1000 mPa·s,         -   a total nitrogen content at least equal to 0.6% and at most             equal to 1.6%, these percentages being expressed by dry             weight relative to the dry weight of composition,         -   a pH below 9.

The T test, used to measure the viscosity of a liquid composition of amylaceous material, consists firstly in determining, by any conventional method within the scope of those skilled in the art, the dry matter of said composition. After this, the dry matter is adjusted in such a way that it is equal to 10%. Finally, the Brookfield viscosity of the composition in question, at 25° C. and at 20 revolution/minute, is measured, said composition thus having a DM of 10%.

More specifically, this suspension is characterized in that it contains, as % by weight:

-   -   a) from 20% to 80% of water,     -   b) from 20% to 80% of a filler which is titanium dioxide,     -   c) from 0.1% to 5%, preferentially from 0.5% to 2%, of a liquid         composition of cationic amylaceous material having:         -   a dry matter by weight of between 10% and 50%,         -   a viscosity, determined according to a T test, of greater             than 200 mPa·s and at most equal to 1000 mPa·s,         -   a total nitrogen content at least equal to 0.6% and at most             equal to 1.6%, these percentages being expressed by dry             weight relative to the dry weight of composition,         -   a pH below 9.

This suspension is also characterized in that the liquid composition of cationic amylaceous material has a dry matter by weight of preferentially between 10% and 30%.

This suspension is also characterized in that the liquid composition of cationic amylaceous material has a pH of between 3.5 and 8.5.

This suspension is also characterized in that the origin of the amylaceous material is potato, corn, wheat, pea, or mixtures thereof.

This suspension is also characterized in that the titanium dioxide is of rutile or anatase origin, and preferentially rutile origin.

This suspension is also characterized in that it can also contain talc, calcium carbonate in natural or synthetic form, and mixtures of these fillers.

In one very specific variant, this suspension is characterized in that the filler is the FP 290 Opacity Pigment product sold by the company FP Pigments™.

In one very specific variant, the suspension is also characterized in that the liquid composition of cationic amylaceous materials is chosen from the Vector™ SC20157 and Vector™ SC 2015 products sold by the company Roquette™.

Another subject of the present invention consists of a method for producing an aqueous suspension of a filler and a cationic amylaceous material by mixing between:

-   -   a) water,     -   b) a filler which is titanium dioxide,     -   c) a liquid composition of cationic amylaceous material having:         -   a dry matter by weight of between 10% and 50%,         -   a viscosity, determined according to a T test, of greater             than 200 mPa·s and at most equal to 1000 mPa·s,         -   a total nitrogen content at least equal to 0.6% and at most             equal to 1.6%, these percentages being expressed by dry             weight relative to the dry weight of composition,         -   a pH below 9.

In this method, the content by weight of the constituents, and the characteristics of the filler and of the liquid composition of cationic amylaceous material, are those already described previously.

Another subject of the present invention consists of a method for producing a paper or a cardboard, by using an aqueous suspension according to the present invention, either in the coating step or in the wet end of production of the sheet.

A final subject of the present invention consists of a paper or a cardboard obtained by using an aqueous suspension according to the present invention, either in the coating step, or in the wet end of production of the sheet. 

1. An aqueous suspension containing: a) water, b) a filler which is titanium dioxide, c) a liquid composition of cationic amylaceous material having: a dry matter by weight of between 10% and 50%, a viscosity, determined according to a T test, of greater than 200 mPa·s and at most equal to 1000 mPa·s, a total nitrogen content at least equal to 0.6% and at most equal to 1.6%, these percentages being expressed by dry weight relative to the dry weight of composition, a pH below
 9. 2. The aqueous suspension as claimed in claim 1, characterized in that it contains, expressed as % by weight of each of its constituents: a) from 20% to 80% of water, b) from 20% to 80% of a filler which is titanium dioxide, c) from 0.1% to 5%, preferentially from 0.5% to 2%, of a liquid composition of cationic amylaceous material having: a dry matter by weight of between 10% and 50%, a viscosity, determined according to a T test, of greater than 200 mPa·s and at most equal to 1000 mPa·s, a total nitrogen content at least equal to 0.6% and at most equal to 1.6%, these percentages being expressed by dry weight relative to the dry weight of composition, a pH below
 9. 3. The aqueous suspension as claimed in claim 1, characterized in that the liquid composition of cationic amylaceous materials has a dry matter by weight of preferentially between 10% and 30%.
 4. The aqueous suspension as claimed in claim 1, characterized in that the liquid composition of cationic amylaceous materials has a pH of between 3.5 and 8.5.
 5. The aqueous suspension as claimed in claim 1, characterized in that the origin of the amylaceous materials is potato flour, corn, wheat, pea, or mixtures thereof.
 6. The aqueous suspension as claimed in claim 1, characterized in that the titanium dioxide is of rutile or anatase origin, and preferentially rutile origin.
 7. The aqueous suspension as claimed in claim 1, characterized in that it can also contain talc, calcium carbonate in natural or synthetic form, and mixtures of these fillers.
 8. A method for producing an aqueous suspension of a filler and a cationic amylaceous material by mixing between: a) water, b) a filler which is titanium dioxide, c) a liquid composition of cationic amylaceous material having: a dry matter by weight of between 10% and 50%, a viscosity, determined according to a T test, of greater than 200 mPa·s and at most equal to 1000 mPa·s, a total nitrogen content at least equal to 0.6% and at most equal to 1.6%, these percentages being expressed by dry weight relative to the dry weight of composition, a pH below
 9. 9. A method for producing a paper or a cardboard, by using an aqueous suspension as claimed in claim 1, either in the coating step or in the wet end of production of the sheet.
 10. A paper or a cardboard obtained by using an aqueous suspension as claimed in claim 1, either in the coating step or in the wet end of production of the sheet.
 11. The aqueous suspension as claimed in claim 2, characterized in that the liquid composition of cationic amylaceous materials has a dry matter by weight of preferentially between 10% and 30%.
 12. The aqueous suspension as claimed in claim 2, characterized in that the liquid composition of cationic amylaceous materials has a pH of between 3.5 and 8.5. 